Chapter 5 · ICSE Class 8 Chemistry (Selina Concise)

Language of Chemistry

Deepen your skills in writing chemical formulae, balancing equations, and using valency.

🔤 Chapter 5

A balanced chemical equation for the formation of water The equation 2 hydrogen gas plus oxygen gas yields 2 water, balanced so that 4 hydrogen atoms and 2 oxygen atoms appear on each side 2H₂ + O₂ → 2H₂O Both sides: 4 H atoms, 2 O atoms — balanced!
5.1

Balancing Chemical Equations

A balanced equation has the same number of atoms of each element on both sides, following the law of conservation of mass.

1

Balance: H₂ + O₂ → H₂O

2H₂ + O₂ → 2H₂O

2

Why must chemical equations always be balanced?

Because atoms cannot be created or destroyed in a reaction, only rearranged

5.2

Using Valency to Write Formulae

The valency of elements determines how many atoms combine — cross the valencies of two elements to write a balanced formula.

1

Calcium has valency 2, chlorine has valency 1. Write the formula for calcium chloride.

CaCl₂

2

Aluminum has valency 3, oxygen has valency 2. Write the formula for aluminum oxide.

Al₂O₃

Practice

Exercises

1. Balance: N₂ + H₂ → NH₃

2. Balance: Mg + O₂ → MgO

3. Sodium has valency 1, oxygen has valency 2. Write the formula for sodium oxide.

4. Magnesium has valency 2, chlorine has valency 1. Write the formula for magnesium chloride.

5. Why is it important to balance equations before interpreting a reaction?

Next chapter — Chemical Reactions 🧫 →